The present invention relates to a laser survey instrument, by which it is possible to form a horizontal reference plane, in particular to form an arbitrary tilt setting plane tilted at a given angle with respect to the horizontal reference plane using a laser beam.
A laser survey instrument is currently used to provide a horizontal reference level for a wide range instead of an optical level.
In this type of laser survey instrument, a laser beam is irradiated in a horizontal direction to thereby form a horizontal reference line, or a laser beam is irradiated in a horizontal direction via a rotating prism, and a horizontal reference plane is formed.
In architectural engineering work and civil engineering work, positioning and setting of a horizontal level are performed by utilizing the horizontal reference plane. For example, a laser beam is detected by a photodetetor to determine a reference position, or it is used for marking-out to determine a position to mount a window in construction of the interior or to set horizontality of a ceiling.
As the present applicant proposed in Japanese Patent Publication Laid-Open No.6-26861, the laser survey instrument of this type is used not only for the setting of the horizontal level but also for the setting of the tilting level, and it is applied in construction work such as inclined drainage system on road or in setting a gradient on road.
Description is now given on a laser irradiation unit 4 of a laser survey instrument disclosed in Japanese Patent Publication Laid-Open No.6-26861, referring to FIG. 25 to FIG. 32.
At the center of a casing 5, a recess 6 in form of a truncated cone is provided, and a support seat 7 is formed at the center of the recess 6. The support seat 7 has projections 9, which are protruded smoothly with tertiary curved surface at three positions equally divided on inner periphery of a circular through-hole 8.
A laser projector 10 for emitting a laser beam is placed in the through-hole 8, and a head 11 of the laser projector 10 is engaged in and supported by the support seat 7. The lower portion of the head 11 is formed in spherical shape, and this spherical portion 11a is slidably engaged with the three projections 9. The laser projector 10 is supported in such manner that it can be tilted in any direction with respect to a vertical line.
A motor seat 14 is mounted on the head 11, and a scanning motor 15 is arranged on the motor seat 14. A gear 16 is engaged on an output shaft of the scanning motor 15 and is engaged with a scanning gear 17, which will be described later.
The axis of the laser projector 10 is aligned with the head 11 of the laser projector 10, and a mirror holder 13 is rotatably mounted via a bearing 12. The scanning gear 17 is engaged on the mirror holder 13. As described above, the scanning gear 17 is engaged with the gear 16 so that the mirror holder 13 can be rotated around the vertical axis by the scanning motor 15. A pentagonal prism 18 is provided on the mirror holder 13, and a laser beam emitted from the laser projector 10 is irradiated as a reference laser beam 77 in a horizontal direction through a projection window 19.
On the middle portion of the laser projector 10, a sensor supporting shelf 63 is provided, and fixed bubble tubes 20 and 21, serving as tilt detectors for detecting a horizontal line, are arranged on the sensor supporting shelf 63 so that the bubble tubes are laid in directions perpendicular to each other. The fixed bubble tubes 20 and 21 are capacitance detection type electric bubble tubes and issue electric signals corresponding to a tilt angle with the horizontal plane as a reference.
On the lower end of the laser projector 10, a base plate 64 approximately in shape of a right-angled triangle is fixed, and a column 70 is erected near the vertex of the base plate 64, and a ball 67 is fixed on the upper end of the column 70. A right-angled L-shaped tilting base plate 62 is arranged above the base plate 64, and a conical recess 99 is formed at the L-shaped vertex in rear of the tilting base plate 62, and the ball 67 is engaged in the recess 99. The top of the tilting base plate 62 is supported by the column 70, and the tilting base plate 62 is pivotally movable around the ball 67. Further, a spring 68 is arranged between the tilting base plate 62 and the base plate 64. Thus, the conical recess 99 is pressed against the ball 67, and the tilting base plate 62 is pushed in a clockwise direction in FIG. 25.
On the tilting base plate 62, arbitrary angle setting bubble tubes 65 and 66, serving as tilting slope detectors, are provided along lines, which cross each other perpendicularly along the L-shape.
A bearing plate 72 is positioned below the sensor supporting shelf 63, and the bearing plate 72 is protruded from the laser projector 10. On the base plate 64, tilting screws 52 and 53 are rotatably mounted at such positions that these form a triangle with the column 70 as vertex. The upper ends of each of the tilting screws 52 and 53 is rotatably supported by the bearing plate 72.
The lower end of the tilting screw 52 is protruded downward from the base plate 64, and a tilting gear 54 is engaged on a protruded end of the tilting screw 52, and the tilting gear 54 is engaged with a tilting gear 56, which will be described later. The lower end of the tilting screw 53 is protruded downward from the base plate 64. A tilting gear 55 is engaged on a protruded end of the tilting screw 53, and the tilting gear 55 is engaged with a tilting gear 57 to be described later.
A tilting nut 48 is screwed on the tilting screw 52, and a nut pin 50 having circular cross-section is protruded on the tilting nut 48. From the end surface of the tilting base plate 62 closer to the arbitrary angle setting bubble tube 65, a tilting pin 60 having circular cross-section is protruded in parallel to the center line of the arbitrary angle setting bubble tube 65, and the tilting pin 60 is brought into contact with the nut pin 50. Further, two parallel guide pins 71 are bridged between the base plate 64 and the bearing plate 72. The tilting pin 60 is slidably sandwiched by the two guide pins 71 so that rotation of the tilting base plate 62 in a horizontal direction is restricted, while it allows the tilting pin 60 to rotate in a vertical direction and also around the axis of the tilting pin 60.
A tilting nut 49 is screwed on the tilting screw 53, and a nut pin 51 with circular cross-section is protruded on the tilting nut 49. From the end surface of the tilting base plate 62 closer to the arbitrary angle setting bubble tube 66, a tilting pin 61 having circular cross-section is protruded in parallel to the center line of the arbitrary angle setting bubble tube 66, and the tilting pin 61 is brought into contact with the nut pin 51.
A pedestal 73 is vertically erected on the lower surface of the base plate 64, and a tilting detector 23, also serving as a motor base, is fixed on the base plate 64 via the pedestal 73. On the upper surface of the tilting detector 23, tilting motors 58 and 59 are provided. The tilting gear 56 as described above is engaged on an output shaft of the tilting motor 58, and the tilting gear 57 as described above is engaged on an output shaft of the tilting motor 59, and these are engaged with the tilting gears 54 and 55 respectively.
On the lower surface of the tilting detector 23, a ring-like reflection mirror is arranged. At positions opposite to the tilting detector 23, a given number (4 in the present embodiment) of optical sensors 24a, 24b, 24c and 24d each comprising a set of light emitting elements and photodetection elements are arranged on the same circumference around the axis of the laser projector 10 when the casing 5 and the laser projector 10 are at a vertical position.
From the head 11 of the laser projector 10, tilting arms 25 and 26 are elongated in a horizontal direction, and after passing through conical surface of the recess 6, these are positioned inside the casing 5. At the tip of each of the tilting arms 25 and 26, engaging pins 27 and 28 are provided. The engaging pins 27 and 28 are designed in cylindrical shape. The axes of these cylinders cross each other perpendicularly, and a positional relationship is determined in such manner that these are included within a plane, which passes through the spherical center of the spherical portion 11a. For one of the engaging pins 27 and 28, e.g. the engaging pin 27, horizontal movement is restricted, and it is allowed to move only in a vertical direction. Although not shown in the figure, the engaging pin 27 is slidably engaged in a guide groove extending in a vertical direction, or the engaging pin 27 may be slidably pressed against the wall surface extending in a vertical direction by resilient means such as a spring, etc.
On the inner wall of the casing 5, shelf plates 29 and 30 are arranged, and a level adjusting motor 31 is mounted on the shelf plate 29, and a level adjusting motor 32 is mounted on the shelf plate 30. A driving gear 33 is engaged on a rotation shaft of the level adjusting motor 31, and a driving gear 34 is engaged on a rotation of the level adjusting motor 32. A screw shaft 35 running perpendicularly to the engaging pin 27 and bridging between the ceiling of the casing 5 and the shelf plate 29 is rotatably arranged, and a driven gear 36 is mounted on the screw shaft 35. The driven gear 36 is engaged with the driving gear 33. A slide nut 37 is screwed on the screw shaft 35, and a pin 38 is protruded on the slide nut 37 so that the pin 38 and the engaging pin 27 are slidably brought into contact with each other.
Similarly, a screw shaft 39 running perpendicularly to the engaging pin 28 and bridging over the ceiling of the casing 5 and the shelf plate 30 is rotatably provided. A driven gear 40 is mounted on the screw shaft 39 and the driven gear 40 is engaged with the driving gear 34. A slide nut 41 is screwed on the screw shaft 39, and a pin 42 is protruded on the slide nut 41 so that the pin 42 and the engaging pin 28 are slidably brought into contact with each other.
On the ceiling of the casing 5 and between the screw shaft 35 and the screw shaft 39, a spring receptacle 43 is provided, and a spring 44 is mounted between the spring receptacle 43 and the laser projector 10, and the laser projector 10 is pushed clockwise around the support seat 7 in FIG. 25.
In the figure, reference numeral 45 represents a battery box for accommodating a battery to drive the laser survey instrument. The laser irradiation unit 4 of the laser survey instrument as described above is installed on a tripod (not shown) via leveling bolts 46 for leveling purpose. Reference numeral 47 represents a glass window to surround the mirror holder 13.
A control unit of the conventional type instrument is shown in FIG. 30.
The results of the detection by the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 are inputted to an angle detection circuit 87 via a switching circuit 85, and the results of detection of the fixed bubble tube 21 and the arbitrary angle setting bubble tube 66 are inputted to an angle detection circuit 88 via a switching circuit 86. On the angle detection circuits 88 and 87, reference angles 92 and 91 are set respectively. The reference angles 91 and 92 are normally 0.degree..
When a signal from the fixed bubble tube 20 is inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 detects a deviation from the reference angle 91. The signal of the angle detection circuit 87 is inputted to a motor controller 89, which drives and controls the level adjusting motor 31.
When signals from the fixed bubble tube 20 and the arbitrary setting bubble tube 65 are inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 outputs a signal corresponding to the deviation. This signal is inputted to a tilt driving circuit 83, which drives and controls the tilting motor 58. When a signal from the arbitrary angle setting bubble tube 65 is inputted to the angle detection circuit 87 by the switching circuit 85, the angle detection circuit 87 detects a deviation from the reference angle 91. The signal of the angle detection circuit 87 is inputted to the motor controller 89, which drives and controls the level adjusting motor 31.
A signal of the angle detection circuit 88 is inputted to a motor controller 90, which drives and controls the level adjusting motor 32. The signal of the angle detection circuit 88 and the signal from an arbitrary angle setter 82 are inputted to a tilt driving circuit 84, which drives and controls the tilting motor 59.
Angular deviations of the angle detection circuits 87 and 88 are inputted to a discriminator 93. The discriminator 93 selects an angular deviation of the angle detection circuits 87 or 88, whichever is greater, and an output corresponding to the change of the angular deviation thus selected is outputted to a display unit driver 94, which displays a value corresponding to the deviation on a display unit 95.
A reference plane formed by a reference laser beam 77 can be set in a horizontal direction or at any desired angle. In the following, description will be given on leveling operation of the laser survey instrument to form the horizontal reference plane.
When the laser irradiation unit 4 is installed and no adjustment is made yet, the axis of the laser projector 10 is generally not aligned with a vertical line, and the fixed bubble tubes 20 and 21 are not in a horizontal position. By the switching circuits 85 and 86, signals from the fixed bubble tubes 20 and 21 are inputted to the angle detection circuits 87 and 88.
When the reference angles 91 and 92 are 0.degree., angular deviation signals are issued from the angle detection circuits 87 and 88. When the angular deviation signals are issued, the motor controllers 89 and 90 drive the level adjusting motors 31 and 32 in such direction that the angular deviation signal is turned to 0.
Description is now given on an operation relating to one of the level adjusting motors 31 and 32, e.g. the former.
When the level adjusting motor 31 is driven, rotation of the level adjusting motor 31 is transmitted to the screw shaft 35 via the driving gear 33 and the driven gear 36. With the rotation of the screw shaft 35, the slide nut 37 is moved up or down. Upward or downward movement of the slide nut 37 is transmitted to the tilting arm 25 via the pin 38 and the engaging pin 27, and the laser projector 10 is tilted.
As described above, the engaging pin 27 is restricted to move in a horizontal direction, and it is allowed to move only in a vertical direction. Thus, the tilting direction of the laser projector 10 is under restriction, and it is tilted around the axis of the engaging pin 28, which passes through the spherical center of the spherical portion 11a. Next, when the level adjusting motor 32 is driven, the screw shaft 39 is rotated, and the engaging pin 28 is moved up or down via the pin 42.
The movement in a horizontal direction of the engaging pin 27 is restricted by a groove (not shown), and its movement in a vertical direction is restricted by the pin 38 and the spring 44. Accordingly, the engaging pin 27 is allowed only to rotate around the axis of the engaging pin 27, which passes through the spherical center of the spherical portion 11a.
When the pin 42 is moved up or down, being associated with sliding movement in an axial direction between the pin 42 and the engaging pin 28, vertical movement is given to the engaging pin 28, and the laser projector 10 is tilted around the axis of the engaging pin 27. Because cross-section of the engaging pin 27 is circular as described above, titling of the axis of the engaging pin 27 does not change even when the engaging pin 27 is rotated. That is, a tilting operation by each of the level adjusting motors 31 and 32 exerts no influence on the other tilting shaft, i.e. tilting of the axes of the engaging pins 27 and 28. Therefore, a tilt adjustment of one shaft can be independently performed from that of the other shaft, and a tilt adjusting operation and a control sequence relating to the tilt adjusting operation are extremely simplified.
The laser projector 10 is pushed clockwise in FIG. 25 by the spring 44. Accordingly, the laser projector 10 accurately follows after the movement of the slide nut 37.
Because the spherical portion 11a of the laser projector 10 is supported at three points by the projections 9 as described above, when the laser projector 10 is tilted, it is stably supported and does not totter. Because the spherical portion 11a is in contact with the projections 9 having smooth curved surfaces, the laser projector 10 can be moved smoothly and freely in any tilting directions, and posture of the laser projector 10 can be easily adjusted.
When the laser projector 10 is tilted, and a leveling operation proceeds, the detection values of the fixed bubble tubes 20 and 21 are turned closer to those of the horizontal plane. Finally, the angular deviation outputted by the motor controllers 89 and 90 is turned to 0, and the leveling operation is completed.
The detection ranges of the fixed bubble tubes 20 and 21 are narrow. When a given range is exceeded, it is turned to saturation state. Then, a tilting direction can be detected, but the value of the tilt angle cannot be detected. For this reason, the optical sensors 24a, 24b, 24c and 24d are provided in order that the adjusting mechanism comprising the level adjusting motors 31 and 32, the driving gears 33 and 34, the driven gears 36 and 40, the screw shafts 35 and 39, the slide nuts 37 and 41, the tilting arms 25 and 26, etc. may not be operated beyond the mechanical adjustment range. Specifically, when mechanical adjustment range is reached, the light emitted from one of the optical sensors 24a, 24b, 24c and 24d is reflected by the reflection mirror provided on the tilting detector 23, and the light is then received by the optical sensor, and it is detected that the limit of the mechanical adjustment range has been reached. Then, the level adjusting motors 31 and 32 are stopped, or it is displayed on the display unit that it is the limit of the mechanical adjustment range, or alarm is issued by buzzer.
When it is turned to such a state, a coarse adjustment is performed to set to the adjustment range using the leveling bolts 46, and the leveling operation is started again.
When the leveling operation has been completed, a laser beam is irradiated from the laser projector 10. Further, by driving the scanning motor 15, the laser projector 10 is rotated around the vertical axis. By irradiating the laser beam in a horizontal direction through the pentagonal prism 18 and by rotating it, a horizontal reference plane is formed by the laser beam.
In the process of the leveling operation, some time is required from the starting to the completion of the leveling. During this period, a progress of the leveling operation is displayed to the operator to notify that the leveling operation is properly performed, thus relieving the operator from feeling uneasiness.
By the discriminator 93, it is judged that the angular deviation outputted from the angle detection circuits 87 and 88 is big or small. The bigger angular deviation is selected, and the condition of the change of the selected angular deviation is outputted to the display unit driver 94. Further, the content of display is changed according to the change of the angular deviation, and it is displayed on the display unit 95.
The bigger angular deviation is selected because more time is required for angular adjustment when the angular deviation is big. Instead of selecting one of big or small angular deviations, a sum of angular deviations outputted from the angle detection circuits 87 and 88 may be obtained, and the content of the display may be changed according to the sum of the angular deviations.
The relationship between the angular deviation and time is as shown in FIG. 31. Based on this relationship, the position to change the display content is set in advance. When it is turned to the position where the angular deviation has been set, the display is switched over, and the progress of the leveling operation is notified to the operator.
Next, description will be given on the case where, after the horizontal reference plane has been formed, the reference plane formed by the reference laser beam 77 is set to an arbitrary angle.
By the arbitrary angle setters 81 and 82, numerical values to tilt the reference plane are inputted to the tilt driving circuits 83 and 84 respectively.
Then, it is judged whether the detection results of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 are identical with those of the fixed bubble tube 21 and the arbitrary angle setting bubble tube 66, and it is tried to equalize the results. In this case, it is preferable that the fixed bubble tubes 20 and 21 are at a horizontal position, but they may not be necessarily at a horizontal position and it will be all right if they are not in saturated state.
When the outputs of the fixed bubble tubes 20 and 21 and the outputs of the arbitrary angle setting bubble tubes 65 and 66 agree with each other, the arbitrary angle setting bubble tubes 65 and 66 are tilted so that they are aligned with the angles set by the arbitrary angle setters 81 and 82. Further, the laser projector 10 is tilted so that the arbitrary angle setting bubble tubes 65 and 66 are turned to a horizontal position. Then, the rotation axis of the laser projector 10 is turned to such position as to form the arbitrary angle reference plane as desired. By rotating the laser projector 10, the laser beam reference plane as desired is formed.
More concrete description will be given below. Because an angle setting operation to the arbitrary angle setting bubble tube 65 is the same as the angle setting operation to the arbitrary angle setting bubble tube 66, description will be given below only on the arbitrary angle setting bubble tube 65.
To the switching circuit 85, a switching signal is inputted from an input unit or a control unit (not shown), and a signal from the fixed bubble tube 20 and a signal from the arbitrary angle setting bubble tube 65 are inputted to the angle detection circuit 87. On the angle detection circuit 87, a deviation of the angles detected by the two bubble tubes 20 and 65 is obtained. If there is a deviation, the deviation signal is inputted to the tilt driving circuit 83.
The tilt driving circuit 83 drives the tilting motor 58. Driven by the tilting motor 58, the tilting gear 56 is rotated, and the rotation of the tilting gear 56 is transmitted to the tilting screw 52 via the tilting gear 54, and the tilting nut 48 is moved up or down in a desired direction. The nut pin 50 of the tilting nut 48 is engaged with the tilting pin 60, and the tilting base plate 62 is tilted in such direction that the deviation is turned to 0.
The tilting of the tilting base plate 62 is detected by the arbitrary angle setting bubble tube 65, and it is inputted to the angle detection circuit 87 via the switching circuit 85.
By the angle detection circuit 87, a deviation between detected angles of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 is calculated. The detection angle deviation is fed back to the tilt driving circuit 83, and the titling motor 58 is driven until the detection angle deviation is turned to 0.
When the detection angle deviation is turned to 0, the axis of the laser projector 10 is perpendicular to the plane detected by the arbitrary angle setting bubble tubes 65 and 66.
Next, the setting angle is inputted to the tilt driving circuit 83 by the arbitrary angle setter 81, and a tilt reference plane setting operation is started.
On the tilt driving circuit 83, the tilting motor 58 is driven in such manner that it is turned to an angle corresponding to the setting angle inputted by the arbitrary angle setter 81, and the tilting base plate 62 is tilted in a direction reverse to the tilt reference plane to be obtained.
Here, for example, a pulse motor is used as the tilting motor 58. The tilt angle of the tilting base plate 62 and the number of pulses of the pulse motor necessary for the tilting are stored in the tilt driving circuit 83 in advance, and the number of pulses corresponding to the angle set by the arbitrary angle setter 81 is outputted to drive the tilting motor 58.
The tilting screw 52 is rotated by the tilting motor 58, and the tilting nut 48 is moved in a desired direction, for example, in a downward direction.
The movement of the tilting nut 48 is transmitted to the tilting base plate 62 via the nut pin 50 and the tilting pin 60 as described above, and the tilting base plate 62 is tilted counterclockwise in FIG. 25 around the ball 67.
As described above, the tilting pin 60 is guided by the guide pin 71 and is tilted only in a vertical direction. Therefore, the tilting of the tilting pin 60 gives no influence on the tilting of the arbitrary angle setting bubble tube 66.
When the tilting base plate 62 is tilted, an output value from the angle detection circuit 87 is changed, and a comparison result calculated by the tilt driving circuit 83 decreases.
When the comparison result is turned to 0, the driving of the tilting motor 58 is stopped, and the tilt setting operation of the tilting base plate 62 is completed. A signal of this completion is also inputted to the switching circuit 85, and the circuit is switched over in such manner that only the signal from the arbitrary angle setting bubble tube 65 is inputted to the reference angle 91.
An tilting operation for the arbitrary angle setting bubble tube 66 is performed in the same manner. Because the tilting pin 60 is guided by the guide pin 71 as described above, the tilting operation of the arbitrary angle setting bubble tube 66 exerts no influence on the arbitrary angle setting bubble tube 65. Therefore, the tilting operation of the tilting base plate 62 in two directions can be controlled independently from each other, and a control sequence relating to the tilting operation of the tilting base plate 62 in two directions is simple.
When the tilt setting operation of the tilting base plate 62 has been completed, the tilting operation of the laser projector 10 is started for setting the tilt reference plane based on the detection result of the arbitrary angle setting bubble tube 65. The setting operation of the tilting of the laser projector 10 is performed in such manner that the detection result of the arbitrary angle setting bubble tube 65 indicates the horizontal direction. The operation is the same as the operation of the case where leveling operation is performed based on the fixed bubble tubes 20 and 21, and detailed description is not given here.
FIG. 29 shows the condition where the setting operation of the tilt reference plane has been completed. When the setting operation of the tilt reference plane is completed, the tilting base plate 62 is at a horizontal position.
A coincident operation of the fixed bubble tube 20 and the arbitrary angle setting bubble tube 65 is performed to guarantee the accuracy of tilting operation of the tilting base plate 62. This may be performed each time the tilting operation is carried out or after it has been repeated by a given times.
FIG. 32 shows an example of a controller 96 where the arbitrary angle setters 81 and 82 are incorporated. The tilting of the tilting base plate 62 is supported by the tilting of two axes of X-Y, and the numerical values thus set are displayed on the display units 97 and 98.
In the above, description has been given under the assumption that adjustment is already completed as to in which direction the reference plane formed by the reference laser beam 77 is tilted. Actually, however, an operation is first performed to accurately set in a direction (in a horizontal direction), in which it is wanted to direct the laser irradiation unit 4 of the laser survey instrument.
In the past, the operation to set in a direction to be tilted has been performed by using a collimator 75 mounted on the upper surface of the laser irradiation unit 4 as shown in FIG. 25. The tilting direction of the tilt setting mechanism in the laser irradiation unit 4 is designed as parallel to the longitudinal direction of the bubble tube for setting and detecting the tilting. Similarly, the collimating direction of the collimator 75 is also designed as to be in parallel. The direction of the laser irradiation unit 4 is also aligned with this. The operation to set the collimator 75 in a direction to be tilted is entirely an operation to rotate or move the laser irradiation unit 4 and to turn the tilting direction of the tilt setting mechanism in the laser irradiation unit 4 and the bubble tube in a given direction. Normally, the laser irradiation unit 4 is mounted on a tripod, and description is given now on operation on the tripod.
An object (not shown) such as a target is installed in advance in a direction, in which the tilting is to be set. By setting the laser survey instrument main body accurately face-to-face to the object using the collimator 75, the direction of the laser irradiation unit 4 is set to a direction, in which it is to be tilted.
The screws (not shown) to fix the laser irradiation unit 4 are loosened, and the laser irradiation unit 4 is rotated. By collimating the object using the collimator 75, the direction of the laser irradiation unit 4 is accurately set to the object.
As it is evident from the above description, the setting of a tilt angle (an angle of elevation) in a series of setting operations of the laser survey instrument is based on the horizontal plane as reference and is performed according to the tilt information electrically detected by the tilt detector such as a bubble tube, and there is no intervention of man-made errors from the person who performs surveying. Therefore, the tilt angle can be set at high accuracy.
However, in the operation to set the laser irradiation unit 4 in a direction to be tilted, the collimator 75 is used, and it is up to man-made or artificial judgment of the survey or to judge whether it actually agrees or not. Further, the collimator 75 originally performs collimation without requiring high-grade technique, and unlike a collimating telescope, its collimation accuracy is not very high. For this reason, in the direction setting using the collimator 75, man-made errors also intervene in addition to low accuracy of the collimator 75 itself, and the setting of direction is not performed at high accuracy. In the conventional type civil engineering work which does not require very high accuracy, there has been no problem in the direction setting by the collimator 75, while, in the highly mechanized civil engineering work performed in recent years, high accuracy is required, and the problem of accuracy arises.